Abstract
Hydrogen peroxide and peroxymonocarbonate anion-based bleach reactions are important for many applications such as paper bleach, waste water treatment and laundry. Nonheme iron(III) complexes, [Fe III (L 1-4 )Cl 2 ] with the 1,3-bis(2 ′ -Ar-imino)isoindolines ligands (HL n , n=1–4, Ar = pyridyl, thiazolyl, benzimidazolyl and N-methylbenzimidazolyl, respectively) have been shown to catalyze the oxidative degradation of morin as a soluble model of a bleachable stain by H 2 O 2 in buffered aqueous solution. In these experiments the bleaching activity of the catalysts was significantly influenced by the Lewis acidity and redox properties of the metal centers, and showed a linear correlation with the Fe III /Fe II redox potentials (in the range of 197–415 mV) controlled by the modification of the electron donor properties of the ligand introducing various aryl groups on the bis-iminoisoindoline moiety. A similar trend but with low yields was observed for the disproportionation of H 2 O 2 (catalase-like reaction) which is a major side reaction of catalytic bleach with transition metal complexes. The effect of bicarbonate ions might be explained by the reduction of Fe(III) ions and/or the formation of peroxymonocarbonate monoanion, which is a much stronger oxidant and could increase the formation of the catalytically active high-valent oxoiron species.
Highlights
Oxidation reactions including low-cost and nontoxic transition metallic catalysts and green oxidants such as H2O2 have been extensively studied [1,2,3,4]
We have shown that the activity of the catalysts is significantly influenced by the Lewis acid and redox properties of the metal centers which can be controlled by varying the aryl substituent on the bis-iminoisoindoline moiety
First we investigated the effect of the pH value of the aqueous solution and found that the best activity was observed at pH 10 for 1 (Figure 1)
Summary
Oxidation reactions including low-cost and nontoxic transition metallic catalysts and green oxidants such as H2O2 have been extensively studied [1,2,3,4]. As a continuation of these studies, efforts have been made to evaluate the bleaching potential of our previously prepared [FeIII(L1−4)Cl2] complexes by the use of morin as a model compound for bleaching stain, to understand how the parameters influence the activity and how the catalytic activity can be optimized compared to our manganese system (Scheme 1). These kinds of catalytic systems are increasingly important for many applications such as pulp and paper bleach and waste water treatment
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